The present invention relates generally to the packaging of portable peripheral cards and more particularly to the manufacture of peripheral cards such as PCMCIA cards having injection molded packages that are formed from a molding compound that includes an organic polymer laden filler material.
The widespread use of personal computers has brought about a subsequent demand for expansion boards to enhance theft functions. Originally, these boards were mounted internally. Thus, to replace or add new boards, one had to open the computer. However, the advent of the laptop personal computer and handheld computers brought about the development of the portable expansion board called a peripheral card. "PCMCIA", also known as PC cards, refers to an industry standard for packaging certain peripheral cards. PCMCIA cards are inserted in external slots of a laptop or handheld computer without the inconvenience of opening the computer. Their small size and portability allow easy interchange of applications by merely plugging and unplugging different peripheral cards into the external slots of the computer or other electronic device. Common applications available in PCMCIA format include modems, wireless communicators, and memory boards.
A PCMCIA card 10 constructed in a conventional fashion is depicted in FIG. 1. A printed circuit board 15 is electrically coupled to a female PCMCIA connector 20. If the card contains a wireless communicator, the card typically must include radio frequency (RF) shields 25 to prevent RF interference with the computer. The printed circuit board 15 fits in a groove or shelf in a plastic rim 30 that surrounds the circuit board. Sheet metal jackets 35 are attached to the top and bottom of the assembly to form the complete PCMCIA card 10. The metal jackets 35 do provide some RF shielding, but their primary purpose is to provide structural integrity.
Unfortunately, the process of assembling this conventional peripheral card and the assembled card itself possess certain drawbacks. First, the manufacturing process must align and attach several parts: the board, the edge connector, the plastic rim, the RF shields, and the metal jackets. This multi-stage assembly process is time consuming and labor intensive and therefore quite costly. Second, the use of a plastic rim wastes valuable printed circuit board real estate. Third, the sheet metal jackets are generally fairly flexible implying a relatively weak external protective structure for the board.
Replacing the printed circuit board's conventional package with an injected molded package is an effective solution to the preceding disadvantages. Such a portable peripheral card that includes an injected molded package is disclosed in Takiar et al.'s co-pending application Ser. No. 08/275,985 now U.S. Pat. No. 5,554,821 entitled: Removable Computer Peripheral Cards Having a Solid One-Piece Housing and Method of Manufacturing The Same filed Jul. 15, 1994 which is incorporated by reference herein in its entirety.
In conventional plastic packaged integrated circuits (ICs), the packaging material that is used in the injected mold process is often formed from a molding compound that includes a resin and filler materials. The resin is the base material of the molding compound. The resin may be either a thermoplastic or thermoset type. Filler material is added to this resin material to enhance structural integrity in IC packaging applications. Fused or crystalline SiO.sub.2 (silica) or glass fibers often serve as the filler material. As well as improving the mechanical strength of the molding compound, such filler material also reduces the thermal coefficients of expansion, and, therefore, reduces the molding compound's shrinkage after molding. Small amounts of coupling agents, coloring agents, flame retardants, placticizers, and wax may also be added to optimize the molding compound as required. Additionally, hardeners and catalysts may be combined with the thermoset resin.
One potential filler material for the described molded peripheral card would naturally be silica since such fillers are commonly used in IC packages. Although such an injected molded package is advantageous for most peripheral card applications, this package does possess certain potential drawbacks for some applications. First, if the filler material is made entirely of silica and constitutes 60 to 70% by volume of the entire molding compound, a peripheral card with an injected molded package will weigh more than a conventional card with a relatively lighter sheet metal jacket. Accordingly, when the injected molded card is inserted into certain card slots, the slot ejection mechanism may have difficulty ejecting the heavier card. Second, the relatively high weight of the silica filler material combined with the silica's relatively high brittleness may result in the card being susceptible to breakage during certain types of stress, such as when one drops the card.
Thus, a way to reduce the weight, brittleness, and warpage and optimize the stress properties of the molding compound is highly desirable. Accordingly, the general objective of the present invention is to decrease the weight, brittleness, and warpage of the molding compound while allowing one to easily balance and optimize the molding compound's, as well as the entire card's, stress, weight, brittleness, and warpage properties.